#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
#define print_int_expr_and_value(n)            printf("%6s == %d\n", (#n), (n))

int round_to_nearest_multiple_of_10(int n) {
    int n_rounded; // not initialized because will be initialized in either if clause or else clause
    if(n % 10 <= 4) {  // if last digit is 0, 1, 2, 3, or 4...
        n_rounded = (n / 10) * 10; // round down
    }
    else {
        n_rounded = (n / 10) * 10 + 1; // round up  ... <<<<<<<<<<< BUG <<<<<<<<<<<<
    }
    assert(n_rounded % 10 == 0);  // n_rounded must be a multiple of 10, or else we have a bug
    return n_rounded;
}

int main(int argc, char* argv[]) {
    print_int_expr_and_value( round_to_nearest_multiple_of_10(23) );
    print_int_expr_and_value( round_to_nearest_multiple_of_10(27) );
    return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */